Meniscus Prosthetic Devices with Anti-Migration or Radiopaque Features

ABSTRACT

A prosthetic device for use as an artificial meniscus is disclosed. The prosthetic device restores stress distribution, stability, and function to the knee joint after removal of the damaged natural meniscus. In some embodiments, the prosthetic device includes an anti-migration feature that inhibits extreme movement within the joint while permitting free floating over a significant range. In one aspect, the anti-migration feature is an enlarged anterior structure or a posterior meniscus remnant engaging channel while in another aspect, the anti-migration feature includes a tethering member. Still further, removable radiopaque features are provided to enhance trialing of the implant prior to final implantation within the joint.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/945,150, filed Jul. 31, 2020, issued as U.S. Pat. No. 11,439,510,which is a continuation of U.S. patent application Ser. No. 16/153,514,filed Oct. 5, 2018, issued as U.S. Pat. No. 10,736,749, which is acontinuation of U.S. patent application Ser. No. 15/789,145, filed Oct.20, 2017, issued as U.S. Pat. No. 10,092,408, which is a continuation ofU.S. patent application Ser. No. 15/135,250, filed Apr. 21, 2016, issuedas U.S. Pat. No. 9,795,488, which is a division of U.S. patentapplication Ser. No. 14/212,330, filed Mar. 14, 2014, issued as U.S.Pat. No. 9,381,089, which claims priority to and the benefit of U.S.Provisional Patent Application No. 61/785,725, filed Mar. 14, 2013, theentireties of which are hereby incorporated by reference herein.

BACKGROUND

The present disclosure generally relates to medical prosthetic devices,systems, and methods. More specifically, in some instances the presentdisclosure relates to prosthetic devices that replace at least part ofthe functionality of the natural meniscus. Each knee has two menisci, alateral meniscus and a medial meniscus. Each meniscus is acrescent-shaped fibrocartilaginous tissue attached to the tibia at ananterior and a posterior horn. Damage to the meniscus can cause pain andarthritis. Accordingly, in some instances it is desirable to replace thedamaged natural meniscus with a prosthetic device. In some instances theprosthetic devices of the present disclosure are configured to besurgically implanted into a knee joint to replace or augment the naturalmeniscus. It is important that the prosthetic device be of theappropriate size and functionality for the intended patient. Duringimplantation procedures it can be difficult to evaluate movement of themeniscus replacement device in the knee joint. Still further, in certainpatients initial meniscus replacement devices have been expelled fromthe knee joint or were mis-positioned in the first place. Thus, there isa need for meniscus replacement devices that can be more readilyobserved during implantation and retained in its intended place in theknee joint.

While existing devices, systems, and methods have attempted to addressthese issues, they have not been satisfactory in all respects.Accordingly, there is a need for the improved devices, systems, andmethods in accordance with the present disclosure.

SUMMARY

In one embodiment, a floating meniscus prosthetic device is disclosedhaving anti-migration features.

In another embodiment, a prosthetic device for replacing a damagedmeniscus is disclosed. The prosthetic device comprises a central portionhaving an upper surface for engagement with a portion of a femur and anopposing lower surface for engagement with a portion of a tibia. Thecentral portion comprises a resilient material. The prosthetic devicealso includes an outer portion surrounding the central portion andhaving an increased thickness relative to the central portion. The outerportion comprises the resilient material and is tensioned with at leastone reinforcing fiber embedded in the resilient material. The outerportion includes a retention structure sized and shaped to preventposterior migration of the prosthetic device. In one aspect, theretention structure includes a posterior channel configured to engage aposterior remnant of the meniscus. In still a further aspect, thechannel includes a posteriorly extending inferior plow blade configuredto slide under at least a portion of the remnant of the meniscus. Instill a further aspect, the retention structure includes an enlargedanterior flange configured to engage an anterior tibia and/or femoraledge adjacent the joint to inhibit posterior migration. In one feature,the anterior flange has a height that is at least 30 percent greater,and is some embodiments up to 100 percent greater, than the posteriorheight of the prosthetic device. In another aspect, the anterior flangeincludes an inferior extension that is greater than the superiorextension. In an alternative form, the superior extension of theanterior flange is greater than the inferior extension. In yet a furtherform, the retention structure includes one or more fiber reinforcedtethering extensions extending from the outer surface of the prostheticdevice. In one aspect the tethering extensions are loops, while inanother form the extensions are fiber reinforced tabs extendingoutwardly from the sidewall of the device. These tethering extensionscan include fibers, bulk material or both. These loops, when includingfibers, may anchor around the reinforcement fiber.

In another embodiment, a method is provided for replacing the functionof a meniscus within a joint. The method of replacing the meniscusfunction within a joint includes removing a portion of a meniscus withinthe joint and leaving intact a meniscus remnant, then inserting a freefloating meniscus replacement implant into the joint and engaging themeniscus replacement implant with the meniscus remnant such that themeniscus replacement implant is at least in part retained within thejoint by the meniscus remnant. In a further aspect, the meniscusreplacement implant includes a retention channel within the sidewall ofthe implant and the method of engaging the meniscus replacement implantwith the meniscus remnant includes aligning the retention channel withthe meniscus remnant. In still a further feature, the retention channelis a retention channel formed in a posterior portion of a knee meniscusreplacement implant and the engaging includes aligning the retentionchannel with a posterior portion of the meniscus remnant. In yet afurther aspect, the engaging includes suturing a portion of the meniscusreplacement implant to a portion of the meniscus remnant or to tissue ofthe joint capsule adjacent the joint.

In still a further feature of the present disclosure, a method ofimplanting a prosthetic meniscus device is disclosed that permitsin-vivo trialing of the implant that, if on trialing confirmed to be thecorrect sized implant, will remain in situ as final implantation. Morespecifically, the method includes providing an implant with one or moreremovable radiopaque markers. In one aspect, the radiopaque markersextend around at least a portion of the outer wall perimeter of theprosthetic meniscus device. In still a further feature, the radiopaquemarkers extend completely around the device. The method includespositioning the device, including the radiopaque markers, in the jointand then moving the joint through a range of motion while monitoring themovement of the radiopaque markers via radiographic visualization. Afterit is determined that the prosthetic meniscus implant functions properlywithin the joint, the radiopaque markers are removed. In one aspect, theradiopaque markers include a retention assembly and the retentionassembly is released in vivo and the radiopaque markers are removed fromthe device while the device is positioned in the joint. In one aspect,the radiopaque markers are thin sheets of material. In another form, theradiopaque markers include radiopaque filaments.

In yet a further aspect of the present disclosure, a prosthetic meniscusdevice is provided with a removable radiopaque marker assembly. In oneaspect, the radiopaque marker assembly is provisionally retained on theouter side walls of the device. In another form, the radiopaque markerassembly includes an external retention assembly configured for in vivorelease such that the retention assembly can be released while thedevice is positioned within a joint.

BRIEF DESCRIPTION OF DRAWINGS

Other features and advantages of the present disclosure will becomeapparent in the following detailed description of embodiments of thedisclosure with reference to the accompanying of drawings, of which:

FIGS. 1A and 1B are diagrammatic perspective views of a right kneejoint.

FIG. 2 is a diagrammatic side view of a right knee joint.

FIG. 3 is a diagrammatic perspective view of a prior art left medialprosthetic device.

FIG. 4 is a diagrammatic cross-sectional view of the prosthetic deviceof FIG. 3 .

FIGS. 5A-6B are diagrammatic illustrations of a prosthetic device of afirst embodiment positioned in the knee joint.

FIGS. 7A-8B are diagrammatic illustrations of a prosthetic device of asecond embodiment positioned in the knee joint.

FIG. 9 is a diagrammatic cross-sectional illustration of a prostheticdevice of a third embodiment.

FIGS. 10-13B are diagrammatic illustrations of a prosthetic device of afourth embodiment associated with the knee joint.

FIGS. 14-17B are diagrammatic illustrations of a prosthetic device of afurther embodiment associated with the knee joint.

FIGS. 18-21B are diagrammatic illustrations of a prosthetic device of astill a further embodiment associated with the knee joint.

FIGS. 22-23 illustrate a pre-formed core component for a left medialmeniscus replacement device.

FIG. 24 is a diagrammatic cross-sectional view of an implant includingtethering loops.

FIGS. 25A and 25B are diagrammatic perspective views of a left medialmeniscus implant having tethering loops.

FIGS. 26-28 are diagrammatic illustrations showing implantation of aright medial meniscus replacement device including tethering loops.

FIGS. 29-31 illustrate a radiopaque trialing assembly associated with ameniscus replacement device.

FIGS. 32A and 32B illustrate a further radiopaque trialing assemblyassociated with a meniscus replacement device.

FIGS. 33A and 33B illustrate a still further radiopaque trialingassembly associated with a meniscus replacement device.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the illustrated embodiments. It is nevertheless understood thatno limitation of the scope of the disclosure is intended. Any and allalterations or modifications to the described devices, instruments,and/or methods, as well as any further application of the principles ofthe present disclosure that would be apparent to one skilled in the artare encompassed by the present disclosure even if not explicitlydiscussed herein. Further, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure.

Referring now to FIG. 1A, there is shown a top view of a knee joint withan injured meniscus 10. The illustrated meniscus 10 has a tear betweentorn segments 12 and 13 extending from an undamaged remainder 14. Themeniscus includes an outer rim 15 that is anchored to the bone along theposterior rim 20 and the anterior rim 22. Referring to FIG. 1B, the tornsegments 12 and 13, along with the undamaged central meniscus 14 havebeen removed to expose the underlying tibia 35 and define animplantation area 30. The implantation area 30 is bounded by sidewall21. FIG. 2 illustrates a side view of a knee joint between femur 202 andtibia 204. A partial meniscus having anterior portion 205 and posteriorportion 203 shown extending between the adjacent bones.

Referring now to FIGS. 3 and 4 shown therein is a prosthetic device 100according to a prior design set forth in U.S. Pat. No. 8,361,147, whichis hereby incorporated by reference in its entirety. Generally, theprosthetic device 100 is for the replacement of a meniscus that has beenpartially or totally meniscectomized before, damaged, ruptured,disintegrated, diseased, or is otherwise in need of replacement. Forillustrative purposes, the prosthetic device 100 will be described inconjunction with a left knee, medial meniscus replacement. However,corresponding embodiments are utilized for replacement of any of theother menisci, such as the right knee medial meniscus, left knee lateralmeniscus, and/or right knee lateral meniscus. In that regard, the size,shape, thickness, material properties, and/or other properties of theprosthetic device may be configured for each particular application.

The prosthetic meniscus 100 comprises an outer body portion 108 and acentral body portion 110. Generally, the outer body portion 108 has anincreased thickness and height relative to the central body portion 110.In some instances the outer body portion 108 has a thickness between 5mm and 15 mm. In some instances, the central body portion 110 has athickness between 0.5 mm and 5 mm. In one particular embodiment, theouter body portion 108 has a maximum thickness of approximately 10 mmand the central body portion 110 has a maximum thickness ofapproximately 2 mm. The height or thickness of the outer body portion108 varies around the perimeter of the prosthetic device 100 in someinstances. In that regard, the variations in the height or thickness ofthe outer body portion 108 are selected to match the anatomical featuresof the patient in some embodiments. Similarly, the height or thicknessof the central body portion 110 varies across the prosthetic device 100in some embodiments. Again, the variations in the height or thickness ofthe central body portion 110 are selected to match the anatomicalfeatures of the patient in some embodiments. In some embodiments, theprosthetic device 100 is inserted in an insertion configuration and thenloaded, stretched, moved, and/or otherwise transferred to animplantation configuration. In some embodiments the transformationbetween the insertion configuration and the implantation configurationis facilitated through the loading of the prosthetic device 100. In suchembodiments, the variations in height or thickness of the outer andcentral body portions 108, 110 are selected to accommodate thedeformation or transformation between the insertion configuration andthe implantation configuration.

In the illustrated embodiment, the prosthetic device 100 is configuredfor use without a fixation member or fixation device that wouldpenetrate an adjacent bone and/or soft tissue to keep the prostheticdevice in place. Rather, the prosthetic device 100 is configured to“float” within the knee joint without being secured by such bone and/orsoft tissue-penetrating fixation devices or otherwise rigidly fixed tothe femur or tibia and/or surrounding soft tissue. To that end, theouter body portion 108 of the prosthetic device 100 is shaped and sizedto prevent unwanted expulsion of the prosthetic device 100 from the kneejoint. The prosthetic device 100 is implanted into a patient withoutcausing permanent damage to the patient's tibia or other bone and/orsoft tissue structure(s) engaged by the prosthetic device in someembodiments. In some instances the prosthetic device 100 is implanted toalleviate the patient's knee problems while avoiding permanentdestruction of the patient's anatomy, such as cutting or reaming a largeopening in the tibia. In such instances, the prosthetic device 100 maybe subsequently removed and replaced with another prosthetic device ortreatment without adversely affecting the subsequent treatment.

To this end, the outer body portion 108 of the prosthetic device 100includes a first portion 112 and a second portion or bridge 114. In someembodiments, the first portion 112 substantially matches the shape of anatural meniscus. In some embodiments, the outer body portion 108 has asemi-ellipsoidal shape. Accordingly, the first portion 112 extendsaround a majority of the outer body portion 108. The bridge 114 connectsthe two ends of the first portion 112. Thus, where the prosthetic deviceis configured for use as a medial meniscus device, the bridge 114extends along the lateral side of the device. Where the prostheticdevice 100 is configured for use as a lateral meniscus device, thebridge 114 extends along the medial side of the device. Accordingly, theouter body portion 108—comprised of the first portion 112 and the bridge114 and having an increased thickness relative to the central bodyportion 110—completely surrounds the central body portion 110 and servesto limit movement of the prosthetic device 100 after implantation. Thatis, the increased height of the outer body portion 108 along with thecontact pressure on the prosthetic device 100 from being positionedbetween the femur and the tibia prevents the prosthetic device frommoving outside of the desired range of positions within the knee joint.

The height or thickness of the bridge component 114 is based on the sizeof the femur notch and the distance to the cruciate ligaments in someembodiments. In some embodiments, the bridge 114 has a maximum height orthickness that is between ¼ and ¾ the maximum height or thickness of thefirst portion 112 of the outer body portion 108. In some embodiments,the size and shape of the bridge 114 is selected to achieve an optimalpressure distribution on the tibial plateau in order to mimic thepressure distribution of a healthy natural meniscus. The bridge 114 and,more generally, the outer body portion 108 are geometricallycharacterized by anterior, posterior, lateral-anterior, mid-lateral andlateral-posterior angles and heights as well as sagittal and coronalradii of curvature. Further, the outer body portion 108 and the centralbody portion 110 are shaped and sized such that the prosthetic device100 is self-centering. That is, the shape and size of the prostheticdevice 100 itself encourages the prosthetic device 100 to position oralign itself with a desired orientation within the knee joint.Accordingly, as the prosthetic device 100 moves through a range ofpositions within the knee joint it naturally returns to the desiredorientation due to the shape and size of the outer and central bodyportion 108, 110. In some embodiments, the outer body portion and, morespecifically, the bridge 114 acts as a physical barrier limiting themovement of the prosthetic device caused by joint reaction forces. Theself-centering or self-aligning mechanism combined with the prostheticdevice's ability to move within the knee joint results in improvedlocation of the prosthetic device 100 during typical gait cycles (e.g.,flexion-extension angles of 0° to 120° or “heel-strike” to “toe-off”).The result is that the prosthetic device 100 exhibits a load pressuredistribution similar to that of a natural meniscus.

The central body portion 110 defines an upper surface 116 and a lowersurface 118. The upper and lower surfaces 116, 118 are both loadedsurfaces. In particular, the upper and lower surfaces 116, 118 areconfigured to movingly engage with the femur and tibia, respectively. Inthat regard, the prosthetic device 100 can translate and rotate withrespect to the femur and/or tibia within a range. In some instances,translation is possible in both the anterior-posterior andmedial-lateral directions. In some embodiments, the upper surface 116includes both a vertical and horizontal surface. To that end, in someembodiments the upper surface 116 comprises a concave surface thatdefines the vertical and horizontal surfaces. The thickness of thecentral body portion 110 between the upper surface 116 and the lowersurface 118 supports stress distribution capability of the component,while the increased height of the upper surface 116 as it extendsoutwardly towards the outer body portion 108 defines the horizontalsurface of the component. Similarly, in some embodiments the lowersurface 118 includes both vertical and horizontal components. Inparticular, in some embodiments the lower surface 118 comprises a convexsurface. In some embodiments, the upper surface 116 and/or the lowersurface 118 are shaped such that the prosthetic device 100 is biasedtowards a neutral position in the knee. For example, the arcuateprofiles of the upper surface 116 and/or the lower surface 118 areshaped such that the interaction between the surfaces and the cartilageencourages the implant to a particular orientation relative to thesurfaces. This allows the prosthetic device 100 to be self-centering orself-aligning in some embodiments as discussed above with respect to theouter body portion 108.

Referring to FIG. 4 , shown therein is a diagrammatic cross-sectionalview of the prosthetic device 100 taken along an anterior to posteriorsection line between anterior end 113 and posterior end 115. The centralbody 110 is reinforced by pre-tensioned fibers 124 wound around the coreto inhibit outward deformation while allowing inward flexibility. Asshown, the anterior portion 113 of the outer body portion 108 has ananterior height or thickness 160. In that regard, the anterior height orthickness 160 of the anterior end 113 is between about 4 mm andimmediately adjacent bridge structure 114 could be as great as about 15mm and, in some instances, is between about 5.7 mm and about 9.3 mm. Inthe present embodiment, the anterior height or thickness 160 of theanterior end 113 is approximately 7.8 mm. In a smaller embodiment, theanterior height or thickness 160 is approximately 5.7 mm. In a largerembodiment, the anterior height or thickness 160 is approximately 9.3mm. The posterior height or thickness 162 of the posterior end 114 isbetween about 4 mm and immediately adjacent the bridge structure 114could be as great as about 20 mm and, in some instances, is betweenabout 7.7 mm and about 12.7 mm. In the present embodiment, the posteriorheight or thickness 162 of the posterior end 115 is approximately 9.0mm. In a smaller embodiment, the posterior height or thickness 162 isapproximately 7.7 mm. In a larger embodiment, the posterior height orthickness 162 is approximately 12.7 mm.

The anterior portion of the upper surface of the anterior portion 113has an anterior radius of curvature 164. In that regard, the anteriorradius of curvature 164 is between about 10 mm and about 100 mm and, insome instances, is between about 23.0 mm and about 33.1 mm. In thepresent embodiment, the radius of curvature 164 is approximately 72 mm.In another embodiment, the radius of curvature 164 is approximately 28mm. In a smaller embodiment, the radius of curvature 164 isapproximately 23 mm. In a larger embodiment, the radius of curvature 164is approximately 33.1 mm. The posterior portion of the upper surface ofthe posterior portion 115 has a posterior radius of curvature 166. Inthat regard, the posterior radius of curvature 166 is between about 5 mmand about 70 mm and, in some instances, is between about 15.2 mm andabout 24.2 mm. In the present embodiment, the radius of curvature 166 isapproximately 30 mm. In a smaller embodiment, the radius of curvature166 is approximately 15.2 mm. In a larger embodiment, the radius ofcurvature 166 is approximately 24.2 mm.

Further, the anterior portion 113 of the upper surface generally extendsat an anterior angle 168 with respect to an axis 170 extendingsubstantially perpendicular to a plane generally defined by theprosthetic device 100, as shown. The anterior angle 168 is between about45 degrees and about 75 degrees and, in some instances, is between about62 degrees and about 68 degrees. In the present embodiment, the angle168 is approximately 65 degrees. In a smaller embodiment, the angle 168is approximately 62 degrees. In a larger embodiment, the angle isapproximately 68 degrees. The posterior portion 115 of the upper surfacegenerally extends at an posterior angle 172 with respect to an axis 174extending substantially perpendicular to a plane generally defined bythe prosthetic device 100, as shown. The posterior angle 172 is betweenabout 35 degrees and about 70 degrees and, in some instances, is betweenabout 55 degrees and about 61 degrees. In the present embodiment, theangle 172 is approximately 58 degrees. In a smaller embodiment, theangle 172 is approximately 50 degrees. In a larger embodiment, the angle172 is approximately 65 degrees.

The central body portion 110 has a height or thickness 176 between theupper articulation surface 116 and the lower articulation surface 118.In some embodiments, the height or thickness 176 is the minimalthickness of the central body portion 110 and, in more specificembodiments, the minimal thickness of the entire prosthetic device 100.To that end, the height or thickness 176 is between about 1 mm and about3 mm and, in some instances, is between about 1.2 mm and about 2.1 mm.In the present embodiment, the height or thickness 176 is approximately1.5 mm. In a smaller embodiment, the height or thickness 176 isapproximately 1.2 mm. In a larger embodiment, the height or thickness176 is approximately 2.1 mm.

A variety of materials are suitable for use in making the prostheticdevices of the present disclosure. Medical grade polyurethane basedmaterials especially suitable for use in the embodiments describedinclude, but are not limited to, isolated or in combination, thefollowing:

Bionate®, manufactured by DSM, a polycarbonate-urethane is among themost extensively tested biomaterials ever developed. Carbonate linkagesadjacent to hydrocarbon groups give this family of materials oxidativestability, making these polymers attractive in applications whereoxidation is a potential mode of degradation, such as in pacemakerleads, ventricular assist devices, catheters, stents, and many otherbiomedical devices. Polycarbonate urethanes were the first biomedicalpolyurethanes promoted for their biostability. Bionate®polycarbonate-urethane is a thermoplastic elastomer formed as thereaction product of a hydroxyl terminated polycarbonate, an aromaticdiisocyanate, and a low molecular weight glycol used as a chainextender. The results of extensive testing encompassing Histology,Carcinogenicity, Biostability, and Tripartite Biocompatibility Guidancefor Medical Devices verifies the cost effective material'sbiocompatibility.

Another group of suitable materials are copolymers of silicone withpolyurethanes as exemplified by PurSil™, a Silicone Polyether Urethaneand CarboSil™, a Silicone Polycarbonate Urethane. Silicones have longbeen known to be biostable and biocompatible in most implants, and alsofrequently have the low hardness and low modulus useful for many deviceapplications. Conventional silicone elastomers can have very highultimate elongations, but only low to moderate tensile strengths.Consequently, the toughness of most biomedical silicone elastomers isnot particularly high. Another disadvantage of conventional siliconeelastomers in device manufacturing is the need for cross-linking todevelop useful properties. Once cross-linked, the resulting thermosetsilicone cannot be redissolved or remelted. In contrast, conventionalpolyurethane elastomers are generally thermoplastic with excellentphysical properties. Thermoplastic urethane elastomers (TPUs) combinehigh elongation and high tensile strength to form tough, albeit fairlyhigh-modulus elastomers. Aromatic polyether TPUs can have an excellentflex life, tensile strength exceeding 5000 psi, and ultimate elongationsgreater than 700 percent. These materials are often used forcontinuously flexing, chronic implants such as ventricular-assistdevices, intraaortic balloons, and artificial heart components. TPUs caneasily be processed by melting or dissolving the polymer to fabricate itinto useful shapes.

The prospect of combining the biocompatibility and biostability ofconventional silicone elastomers with the processability and toughnessof TPUs is an attractive approach to what would appear to be a nearlyideal biomaterial. For instance, in polycarbonate-based polyurethanes,silicone copolymerization has been shown to reduce hydrolyticdegradation of the carbonate linkage, whereas in polyether urethanes,the covalently bonded silicone seems to protect the polyether softsegment from oxidative degradation in vivo. DSM synthesizedsilicone-polyurethane copolymers by combining two previously reportedmethods: copolymerization of silicone (PSX) together with organic(non-silicone) soft segments into the polymer backbone, and the use ofsurface-modifying end groups to terminate the copolymer chains.

Other applicable materials include PurSil™ silicone-polyether-urethaneand CarboSil™ silicone-polycarbonate-urethane which are truethermoplastic copolymers containing silicone in the soft segment. Thesehigh-strength thermoplastic elastomers are prepared through a multi-stepbulk synthesis where polydimethylsiloxane (PSX) is incorporated into thepolymer soft segment with polytetramethyleneoxide (PTMO) (PurSil) or analiphatic, hydroxyl-terminated polycarbonate (CarboSil). The hardsegment consists of an aromatic diisocyanate, MDI, with low molecularweight glycol chain extender. The copolymer chains are then terminatedwith silicone (or other) Surface-Modifying End Groups. Aliphatic (AL)versions of these materials, with a hard segment synthesized from analiphatic diisocyanate, are also available.

Many of these silicone urethanes demonstrate desirable combinations ofphysical properties. For example, aromatic silicone polyetherurethaneshave a higher modulus at a given shore hardness than conventionalpolyether urethanes—the higher the silicone content, the higher themodulus (see PurSil Properties). Conversely, the aliphatic siliconepolyetherurethanes have a very low modulus and a high ultimateelongation typical of silicone homopolymers or even natural rubber (seePurSil AL Properties). These properties make these materials veryattractive as high-performance substitutes for conventional cross-linkedsilicone rubber. In both the PTMO and PC families, some polymers havetensile strengths three to five times higher than conventional siliconebiomaterials.

Further examples of suitable materials include Surface Modifying EndGroups (SMEs) which are surface-active oligomers covalently bonded tothe base polymer during synthesis. SMEs—which include silicone (S),sulfonate (SO), fluorocarbon (F), polyethylene oxide (P), andhydrocarbon (H) groups—control surface chemistry without compromisingthe bulk properties of the polymer. The result is that key surfaceproperties, such as thromboresistance, biostability, and abrasionresistance, are permanently enhanced without additional post-fabricationtreatments or topical coatings. This technology is applied to a widerange of DSM's polymers.

SMEs provide a series of base polymers that can achieve a desiredsurface chemistry without the use of additives. Polyurethanes preparedaccording to DSM's development process couple endgroups to the backbonepolymer during synthesis via a terminal isocyanate group, not a hardsegment. The added mobility of endgroups relative to the backbonefacilitates the formation of uniform overlayers by the surface-activeend blocks. The use of the surface active endgroups leaves the originalpolymer backbone intact so the polymer retains strength andprocessability. The fact that essentially all polymer chains carry thesurface-modifying moiety eliminates many of the potential problemsassociated with additives.

The SME approach also allows the incorporation of mixed endgroups into asingle polymer. For example, the combination of hydrophobic andhydrophilic endgroups gives the polymers amphipathic characteristics inwhich the hydrophobic versus hydrophilic balance may be easilycontrolled.

Other suitable materials, manufactured by CARDIOTECH CTE, includeChronoFlex® and Hydrothane™.

The ChronoFlex®, polycarbonate aromatic polyurethanes, family ofmedical-grade segmented biodurable polyurethane elastomers have beenspecifically developed by CardioTech International to overcome the invivo formation of stress-induced microfissures.

HydroThane™, hydrophilic thermoplastic polyurethanes, is a family ofsuper-absorbent, thermoplastic, polyurethane hydrogels ranging in watercontent from 5 to 25% by weight. HydroThane™ is offered as a clear resinin durometer hardness of 80A and 93 Shore A. The outstandingcharacteristic of this family of materials is the ability to rapidlyabsorb water, high tensile strength, and high elongation. The result isa polymer having some lubricious characteristics, as well as beinginherently bacterial resistant due to their exceptionally high watercontent at the surface. HydroThane™ hydrophilic polyurethane resins arethermoplastic hydrogels, and can be extruded or molded by conventionalmeans. Traditional hydrogels on the other hand are thermosets anddifficult to process.

Additional suitable materials manufactured by THERMEDICS includeTecothante® (aromatic polyether-based polyurethane), Carbothane®(aliphatic polycarbonate-based polyurethane), Tecophilic® (high moistureabsorption aliphatic polyether-based polyurethane) and Tecoplast®(aromatic polyether-based polyurethane). Tecothane® is a family ofaromatic, polyether-based TPU's available over a wide range ofdurometers, colors, and radiopacifiers. One can expect Tecothane resinsto exhibit improved solvent resistance and biostability when comparedwith Tecoflex resins of equal durometers. Carbothane® is a family ofaliphatic, polycarbonate-based TPU's available over a wide range ofdurometers, colors and radiopacifiers. This type of TPU has beenreported to exhibit excellent oxidative stability, a property which mayequate to excellent long-term biostability. This family, like Tecoflex,is easy to process and does not yellow upon aging. Tecophilic® is afamily of aliphatic, polyether-based TPU's which have been speciallyformulated to absorb equilibrium water contents of up to 150% of theweight of dry resin.

Additional materials of interest include Tecogel, a new member to theTecophilic family, a hydrogel that can be formulated to absorbequilibrium water contents between 500% to 2000% of the weight of dryresin, and Tecoplast®, a family of aromatic, polyether-based TPU'sformulated to produce rugged injection molded components exhibiting highdurometers and heat deflection temperatures.

Additional potentially suitable materials include four families ofpolyurethanes, named Elast-Eon™, which are available from AorTechBiomaterials.

Elast-Eon™ 1, a Polyhexamethylene oxide (PFMO), aromatic polyurethane,is an improvement on conventional polyurethane in that it has a reducednumber of the susceptible chemical groups. Elast-Eon™2, a Siloxane basedmacrodiol, aromatic polyurethane, incorporates siloxane unto the softsegment. Elast-Eon™3, a Siloxane based macrodiol, modified hard segment,aromatic polyurethane, is a variation of Elast-Eon™2 with furtherenhanced flexibility due to incorporation of siloxane into the hardsegment. Elast-Eon™ 4 is a modified aromatic hard segment polyurethane.

Bayer Corporation also produces candidate materials. Texin 4210 andTexin 4215 are thermoplastic polyurethane/polycarbonate blends forinjection molding and extrusion. Texin 5250, 5286 and 5290 are aromaticpolyether-based medical grade materials with Shore D hardness ofapproximately 50, 86, and 90 respectively for injection molding andextrusion.

Except as set forth specifically below, the following exemplar devicesincorporate the features of the prior device described with respect toFIGS. 3 and 4 in terms of materials, function, outer surfaces andpre-tensioned core element as described herein and in more detail inU.S. Pat. No. 8,361,147, hereby incorporated by reference in itsentirety.

Referring now to FIGS. 5A-6B, there is shown a meniscus replacementdevice 200 according to an embodiment of the present disclosure disposedin the joint 206 formed between femur 202 and tibia 204. The device 200includes an anterior end portion 210 and an opposite posterior endportion 212. In the illustrated embodiment, the anterior end portion 210along with the upper surfaces is formed similar to the implant of FIGS.3 and 4 described above and, as discussed more fully below, the implantincludes the fiber reinforcing and pre-tensioning members embeddedwithin the implant to inhibit outward deformation. However, theposterior portion 212 has been modified to form a retention structuredefining a posterior pocket 218. Beginning at transition area 216, theside wall 214 is divided into two fork portions 220 and 226. Forkportion 220 has a lower, inferior surface that extends the farthestposteriorly to define the leading edge 221 of portion 220. Fork portion220 includes an upper, superior surface 222 extending toward the pocketbottom 224 that defines a plow or shovel blade shape. The pocket bottom224 is a concave sidewall defining an inwardly extending recess that isdefined in part by the inferior surface 222 and the superior surface226. The inferior surface of 220 can either be concave, lifting off fromthe surface of the tibia plateau, or convex, following the curve of thetibia plateau. The superior 226 surface of the sidewall terminates atthe upper surface 228 to define a leading tip 229 of the upper surface.The leading tip 229 extends more posteriorly than the upper surface 228such that an overhang structure is created to better define a receivingpocket. In one aspect, the fork portion 220 has lower distal tip 221extends a distance D1 of approximately 3 mm beyond the upper portion tip229. In an alternative form, the upper and lower fork portions extend anequal distance posteriorly. In still a further form, the superior forkportion can extend farther posteriorly than the inferior fork portion.In the illustrated embodiment, the superior surface 222 extends at anangle A with respect to the superior surface of pocket 218. In oneaspect, the angle A is less than 90 degrees, although angle A could beas high as 120 degrees. In still a further aspect, the angle A isapproximately 75 degrees.

As illustrated in FIGS. 6A and 6B, the pocket 218 is configured toengage the posterior rim 20 of the remnants of the meniscus in the kneejoint. The engagement of the posterior rim 20 within the socket 218inhibits extreme movement of the meniscus device 200 posteriorly out ofthe knee joint. However, the device 200 is free to float within thespace 30 as the knee joint moves through its range of motion. As thedevice 200 begins to move posteriorly, the leading fork 220 slides underthe posterior rim 20 and the surface 222 guides the rim into the pocket218.

Referring now to FIGS. 7A-8B, there is shown still a further embodimentof a meniscus replacement device. The meniscus replacement device 200′has many of the same features as the device 200 of FIG. 6A, with theexception that the posterior pocket has been modified. Morespecifically, the distance between the lower posterior edge 221′ and theupper posterior edge 229′ has been increased to a distance D2 ofapproximately 5 mm such that wall 226′ is substantially perpendicular tothe longitudinal axis of the device to form a vertical wall. Theresulting structure has an angle A′ between side wall 226′ and superiorsurface 222′. The angle A′ can have a range similar to angle A describedabove. The resulting structure defines a plow or shovel blade shapehaving leading edge 221′ following by angled surface 222′. As shown inFIGS. 8A and 8 b, the plow blade feature extends under the posterior rim20 and sidewall 226′ engages the posterior rim 20 to inhibit furtherposterior migration of the implant 200′ and/or “jumping” of implant 200on top of the posterior meniscus remnants

In still a further alternative illustrated in FIG. 9 , the implant 240is formed similar to the implant of FIGS. 3 and 4 with an upper surface248 and a further alternative posterior retention structure 242. Morespecifically, the posterior sidewall defines an opening 243 definedbetween two flexible tabs 244 and 245. The opening 243 leads to aninterior passage 249 having an upper channel 246 and a lower channel247. As shown in FIG. 9 , the posterior rim 20 may be inserted throughopening 243 by movement of the flexible tabs 244 and 245. Oncepositioned in the channels 246 and 247, the posterior rim 20 can engagethe implant to inhibit posterior movement as well as engaging theflexible tabs to inhibit anterior movement. Thus, the posteriorretention structure 242 releasably joins the implant 240 to theposterior rim 20 so both will move together during loading cycles as theknee moves through its range of motion.

In a surgical procedure for replacement of a knee meniscus, the kneejoint is prepared to provide an open area 30 as shown in FIG. 1B. Whilea complete rim 15 is shown in FIG. 1B, it is contemplated that thesurgical preparation for implantation of the devices of FIGS. 5A-9 caninclude removal of the majority of rim 15 provided that posterioraspects 20 of the rim are retained. Once the joint space is prepared,the implant is inserted from an anterior opening into the joint spacewith the posterior retention structure oriented posteriorly. The implantis advanced until the posterior retention structure is positionedadjacent the posterior meniscus remnants 20. In one feature, the implantis advanced posteriorly until the blade or wedge 222 slides under theposterior meniscus remnants and they engage the posterior recess of thedevice. In alternative form, the implant is advanced posteriorly untilthe posterior remnants are engaged within the channel 243.

FIGS. 5A-9 illustrate a variety of posterior anti-migration featuresthat are accomplished by posterior wall modifications while stillpermitting the implant to be free floating within the joint. Inalternative configurations shown in FIGS. 10-21B, the implant isinhibited from extreme posterior migration by an anterior anti-migrationstructure defined along the anterior wall of the implant. Morespecifically referring to FIGS. 10-13B, there is shown an implant 250disposed between the femur 202 and the tibia 204. FIG. 11 shows a crosssectional view taken along a plane extending from the anterior toposterior of the joint. The anterior portion 254 is disposed oppositethe posterior portion 252. As explained above, the implant 250 has allof the features of the implant described with respect to FIGS. 3 and 4 ,including a similar posterior portion 252. However, the anterior portion254 has been modified to define an anterior anti-migration structure.The dashed line 258 represents the lower, inferior edge of the implantdisclosed in FIGS. 3 and 4 . Thus, the inferior extension 256 definesthe enhanced anterior anti-migration structure. The anti-migrationstructure 256 includes an inner superior surface 260 for loading againstthe tibia. The surface 260 includes an upper region 262 and a lower,extended region 264 that provides an extra length of wall to engage thetibia and prevent the implant from migrating posteriorly within thejoint space. The upper region has a height 263 of approximately 1.5 mm,the lower region has a height 265 of approximately 2.5-4.5 mm giving thesuperior surface 260 an overall height of in the range of approximately3-6 mm. With the addition of the lower extension, the implant has ananterior wall height 269 of 9-14 mm. As will be appreciated, for theillustrated embodiment, the posterior end wall has a height ofapproximately 9.0 mm. Thus, the anterior anti-migration structure 256has a height that is about 50% greater than the height of the posteriorend of the implant. In alternative form, the anterior wall height can bea much as twice as tall as the wall height of the posterior end of theimplant.

Referring now to FIGS. 14-17B, there is shown a further embodiment of animplant 280 with an anterior anti-migration structure 286 according toanother aspect of the present disclosure. The portions of the implant280 extending between the anterior end 282 and posterior end 284 aresubstantially the same as described above with the exception of theanti-migration structure 286. The anti-migration structure 286 extendsupwardly to define an inner superior surface 288 configured to engage aportion of femur 202. The dashed line 287 extending across said surface288 illustrates the difference between the height of the superiorsurface 289 existing in the implant shown in FIGS. 3 and 4 and theanti-migration extension surface 290 extending substantially moresuperiorly. More specifically, the superior surface 289 has a height 296of approximately 1.5 mm and the surface 290 has a height 295 of 2.5 to4.5 mm, thereby defining a retention member surface 290 height 297 of3-6 mm. The overall height 298 of the anterior anti-migration structureis 9-13 mm. As will be appreciated, for the illustrated embodiment, theposterior end wall as a height of approximately 9.0 mm. Thus, theanterior anti-migration structure 282 has a height that is about 50percent greater than the height of the posterior end of the implant. Inalternative form, the anterior wall height can be a much as twice astall as the wall height of the posterior end of the implant. Thesuperiorly extending anti-migration structure is configured to engagethe femur to prevent unwanted posterior migration of the implant withinthe knee joint.

Referring now to FIGS. 18-21B, there is shown an implant 300 disposedbetween femur 202 and tibia 204. The portions of the implant 300extending between the anterior end and posterior end 304 aresubstantially the same as described above with the exception of theanti-migration structure 302 formed on the anterior end. Theanti-migration structure 302 includes a superior extension 308 and aninferior extension 306. As shown in FIG. 18 , dashed lines 310 and 311illustrate the height of a prior implant such as that shown in FIGS. 3and 4 . As illustrated, the upper or superior extension 308 begins attransition 314 on the upper edge of the sidewall and transitions to themaximum height at the anterior end. Similarly, the lower or interiorextension 306 begins at transition 312 on the lower edge of the sidewalland transitions to the maximum height at the anterior end.

Referring now to FIGS. 21A and 21B, additional details of the extensions306 and 308 are shown. More specifically, lower extension 306 includes atibial plateau surface 330 having a first portion 332 above the dashedline 311 and a second extension portion 334. The upper extension 308includes a femur surface 320 having a first portion 322 below the dashedline 310 and a second extension portion 324. The distance D2′ betweenthe dashed lines 310 and 311 is approximately 6 mm. The distance D3′between the inferior most portion of extension 306 and the superiorextension 308 is approximately 12-18 mm. As will be appreciated, for theillustrated embodiment, the posterior end wall as a height ofapproximately 9.0 mm. Thus, the anterior anti-migration structure 302has a height that is about two times the height of the posterior end ofthe implant.

In some embodiments, the prosthetic device is a melt mold compositeimplant composed of two biocompatible materials: DSM Bionate®Polycarbonate-Urethane (PCU), 80 Shore A, matrix material and ultra highmolecular weight polyethylene (UHMWPE) reinforcement material (DyneemaPurity). In some particular embodiments, a prosthetic device formed ofPCU and reinforced circumferentially with DSM Dyneema® fibers results ina desirable distribution of loads on the underlying articulationsurfaces of the prosthetic device. Accordingly, referring generally toFIGS. 22-24 aspects and methods of manufacturing such a device will bedescribed.

Referring more specifically to FIGS. 22 and 23 , shown therein is aprosthetic device core 372 surrounded by an outer portion 436. Theprosthetic device core 370 includes an upper articulation surface 376and an opposing lower articulation surface 378. The upper articulationsurface 376 is configured to engage the femur while the lowerarticulation surface 378 is configured to engage the tibia. In someembodiments, the prosthetic device core 372 is formed via an injectionmolding process that substantially limits the defects, imperfections,and/or process residue in and on the articulation surfaces. In thatregard, the articulation surfaces may obtain a smoothness substantiallysimilar to that of the surfaces of the mold in which they are formed. Insome instances, the mold surfaces are mirror polished to an opticalpolish between about 0.05 Ra and 0.4 Ra.

The prosthetic device 370 is imbedded with fibers shown in FIG. 24 . Insome instances, the fibers are positioned circumferentially around theprosthetic device core 372. In that regard, the core 372 includesfeatures to facilitate positioning of the fibers within the prostheticdevice 370 in some embodiments. For example, referring more specificallyto FIG. 23 , shown therein is a diagrammatic perspective view of thecore 372 according to one aspect of the present disclosure. As shown,the core 372 includes an upper rim 380 and a lower rim 382 defining anouter boundary of the core. Between the upper and lower rims 380, 382the core 372 includes a series of alternating projections and recesses.In the current embodiment, the core includes projections 384, 386, 388,and 390 between the upper rim 380 and the lower rim 382. Between therims 380, 382 and the projections the core 372 includes recesses 392,394, 396, 398, and 400. In some embodiments, the recesses 392, 394, 396,398, and 400 are sized and shaped to receive the fibers to be imbeddedwithin the device 370. In some instances, the projections 384, 386, 388,390 and the recesses 392, 394, 396, 398, 400 are configured such thatthe fibers may be wound around the core 372.

As shown in FIG. 23 , a tether loop 450 is shown positioned between thecore 372 and the reinforcing fibers 452. During the manufacturingprocess, one or more loops 450 are positioned adjacent the core 372 andmaintained there while one or more reinforcing fibers are woundcircumferentially around the core. As shown in FIG. 24 , after theover-flow molding process is completed, the reinforcing fibers 438 and aportion of the suture loop 452 are encapsulated into the prostheticimplant. As a further alternative, it can be one or more continuousfibers that go in toward the core and back out again to form externalloops at different locations along the exterior of the implant.

In some embodiments, the fibers are configured to distribute the loadacross the prosthetic device 370 in a manner that mimics a naturalmeniscus. In that regard, the amount of fibers, the type of fibers,distribution of the fibers, and/or the location of the fibers is alteredin some embodiments to achieve a desired load distribution. Further,these attributes of the fiber may vary within a single implant dependingon the position within the implant. For example, in some instances thenumber or density of fibers varies along the height of the prostheticdevice. In some instances, the fiber characteristics are determined atleast partially based on the patient receiving the prosthetic device370. For example, factors such as the size of the patient's kneeanatomy, the patient's weight, the patient's anticipated activity level,and or other aspects of the patient are taken into consideration whendetermining the characteristics of the fibers imbedded in the prostheticdevice 370. In some instances, a fiber incorporation ratio (FIR) istaken into consideration. Generally, the fiber incorporation ratio isrepresentative of the amount or percentage of fibers within theprosthetic device 370 as compared to the matrix material or basematerial. In some embodiments, the fiber incorporation ratio is measuredas the area of the fibers divided by the area of the prosthetic deviceas view in a cross-section of the device, or

${FIR} = {\frac{{Area}_{FiberCS}}{{Area}_{DeviceCS}}.}$

In some embodiments, the resilient matrix material comprises abiocompatible polymer. In some instances, the polymer is a polycarbonatepolyurethane. In one specific embodiment, the matrix material is DSMBionate® Polycarbonate-Urethane (PCU), 80 Shore A. The high modulusreinforcement material utilized in the application may be any one of thefollowing: Ultra High Molecular Weight Polyethylene (UHMWPE) fiber, forexample DSM Dyneema® Purity; Para-aramid synthetic fiber, for exampleDuPont™ Kevlar, Kevlar29, Kevlar49; carbon; stainless-steel; titanium;nickel-titanium (Nitinol); and/or other suitable reinforcementmaterials. In that regard, the fibers may be employed in a monofilamentor multifilament form as a single strand or a multiple fiber twine, in adiameter range of up to 1 mm.

Referring now to FIGS. 25A and 25B, there is shown a further embodimentof a meniscus replacement device 460 according to another aspect of thepresent disclosure. The implant 460 includes tethering loops 450, 454,456 and 458. The loops are formed by a series of fibers loosely woundaround the core 372 after the tension elements discussed with respect toFIGS. 22 and 23 are positioned, with slack portions held outwardlyduring the over-flow molding process to form the loops shown in FIG.25B. Thus, in one form, the loops 450, 454, 456 and 458 are formed of aseries of filaments that are partially embedded within the over moldedarea and partially extending beyond the sidewalls. The loops themselvesmay also include a coating of the over molding material. In one form,each loop has a unique set of filaments extending around the core 376(FIG. 23 ) such that if one loop is cut off, severing of the fibers willnot impact the remaining loops. In still a further form, one or morefiber reinforced tabs extend outwardly from the outer side wall.Although the tabs lack a preformed opening, the tabs provide fiberreinforced areas for the passage of a needle and suture that can firmlyretain the suture without damaging the pliable material of the implant.In one aspect, the tabs are spaced around the implant at strategiclocations similar to FIG. 25B, while in another form, the fiberreinforced tab extends completely around the side wall perimeter of theimplant.

In use, the implant 460 can be inserted into the joint space in aconventional fashion. As shown in FIG. 26 , the anterior tethering loop458 is positioned adjacent the anterior rim 22 and a suture 470 ispassed through the loop 458 and the anterior rim 22. The tension appliedto the suture can be varied to provide the correct amount of freedom ofmovement within the joint space. The other tether loops that are notused can be severed by the physician before implantation in the jointspace. Referring now to FIG. 27 , the implant 460 is positioned in thespaced formed within the remaining portions of the meniscus 15 with thetethering loop 456 positioned adjacent the posterior rim 20. A suture ispassed through the loop 456 and the posterior rim 20 to maintain theimplant within the joint space. In both the tethering arrangements ofFIGS. 26 and 27 , the implant 460 has a high degree of freedom ofmovement with the joint space such that the implant retains its abilityto float freely within the joint to mimic a natural meniscus. In still afurther aspect, the one or more tether loops 454, 456 and 458 areattached to the soft tissue of the joint capsule.

Referring now to FIG. 28 , the implant 460 is more fully tethered in thejoint space by a suture that extends through all or part of the tetherloops 454, 456 and 458 and around the meniscus rim 15 including theposterior rim 20 and the anterior rim 22. In this arrangement, theimplant 460 is constrained to a more limited zone of movement providinga limited range of motion.

Referring now to FIG. 29 , there is shown a diagrammaticallyillustration of an implant 500 similar to those described above incombination with a pair of radiopaque films 510 and 512 having a widthapproximating the thickness of the implant. Such film may include aradiopaque material incorporated into a polymer or other material. Theradiopaque material can include for example, barium sulfate at a 10-30%ratio combined in a polymer matrix. The radiopaque films can bepositioned on the circumference of the implant 500. As shown in FIG. 30, an adhesive strip 514 can be circumferentially wrapped around theradiopaque films to maintain them in position on the implant duringimplantation. As can be appreciated, the implant with the radiopaquefilms can be implanted into the joint space. The knee can be movedthrough a range of motion and the implant monitored by radiographicimaging to determine its positioning in the joint space and whether itwill successfully meet the patient's needs. Once a determination is madethat the implant is satisfactory, an end of the adhesive 514 is peeledfrom the overlap area. Once the end is free, continued movement in thedirection of arrow A will pull the radiopaque films 510 and 512 fromaround the implant and out of the body. In an alternative embodiment 550illustrated in FIGS. 32A and 32B, a radiopaque film or band 570 isdouble circled around the implant 560 with a loop 576 after the firstencirclement of the film. A first end 574 of the radiopaque band 570 ispositioned against the implant 560 and overlapped by at least a portionof the loop 576. A second end 580 is passed back around the implant 560to define an area of overlap area 572 where portion 578 extends over theloop 576. Engagement between the loop and portion 578 in the area ofoverlap 572, along with engagement between the first portion 574 and theloop 576, retains the band in position. The engagement areas can rely onfriction, adhesive or a separate suture or filament to retain the loopand band overlap areas in contact. Although the radiopaque band 570 isshown in a loose configuration for the ease of illustration, it will beappreciated that in most embodiments, the band will be tightened aroundthe outer wall perimeter of the implant 560. In use, the implantassembly 550 is positioned in the knee joint. Once a determination ismade that the implant is satisfactory, the end 580 is pulled in thedirection of arrow A′ to release the adhesive or other retentionmechanism to peel the band from the overlap area 572. Once the end 580is free, continued movement in the direction of arrow A′ will pull theradiopaque film 570 from around the implant and out of the body.

Referring now to FIGS. 33A and 33B, there is shown still a furtherembodiment according to another aspect of the present disclosure. Theimplant 600 has the superior surfaces and retention features discussedabove along with a series of tether loops 610. As illustrated, the loops610 are positioned around the perimeter 606 of the implant 600 with theloops aligned from the top to the bottom of the implant, similar to theembodiments shown in FIGS. 23 and 24 such that the openings along thesides of the loops are oriented generally along the longitudinal axis. Aradiopaque filament 620, such as a wire or thread, is threaded throughthe loops 610 to extend around the perimeter of the device. Radiopaquewires may be formed of or include precious metals, stainless steel,titanium, or nitinol. The filament 620 is tied in a knot 622 to retainthe position of the filament on the implant 600 during implantation.Although a knot is shown, other releasable fixation mechanisms can beused to retain the filament in position. During use, the implant 600 andfilament 620 combination is inserted into the joint. The joint is movedthrough a range of motion and the implant filament 620 is monitored viaradiographic imaging to determine if the implant is performing thedesired function. If the implant 600 is the proper match for thepatient, the knot 622 is undone, and end 624 pulled until the terminalend 626 is removed from the loops 610. In the illustrated embodiment,the loops 610 may be used for tethered anchoring, may be left intact, ormay be cut before final implantation. In this manner, the final implantcan also serve as a trial device allowing the physician to evaluate theimplant performance before final implantation.

Although loops 610 are illustrated as extending outwardly beyond thesidewall of the implant 600 to define an intermittent passage around theperimeter 606 of the implant, it is contemplated that in an alternativeform a channel can be formed in the sidewall of the implant 600 duringthe molding process to provisionally retain the filament 620 inposition.

Although described in the context of a knee meniscus, the compositeimplants described above may be utilized for forming a variety ofprosthetic devices. For example, in some instances the compositeimplants are utilized for knee joints (including meniscus and total kneejoints), hip joints (including acetabular cups), shoulder joints, elbowjoints, finger joints, and other load and/or non-load receivingprosthetic devices. Still further, while embodiments were disclosed withcertain features on anterior and/or posterior portions, it iscontemplated that features from one embodiment, such as a uniqueanterior feature, may be combined with an alternative posterior featuredesign to create a composite implant embodying both the above describedanterior and posterior features from one or more of the implantsdescribed above.

It should be appreciated that in some instances the prosthetic devicesof the present disclosure are formed by other processes than thosedescribed herein. These manufacturing processes include any suitablemanufacturing method. For example, without limitation any of thefollowing manufacturing methods may be utilized: injection moldingincluding inserting inserts; compression molding including insertinginserts; injection-compression molding including inserting inserts;compression molding of prefabricated elements pre-formed by any of theabove methods including inserting inserts; spraying including insertinginserts; dipping including inserting inserts; machining from stocks orrods; machining from prefabricated elements including inserting inserts;and/or any of the above methods without inserts. Further, it should beappreciated that in some embodiments the prosthetic devices of thepresent disclosure are formed of medical grade materials other thanthose specifically identified above. In that regard, in some embodimentsthe prosthetic devices are formed of any suitable medical gradematerial.

While the principles of the present disclosure have been set forth usingthe specific embodiments discussed above, no limitations should beimplied thereby. Any and all alterations or modifications to thedescribed devices, instruments, and/or methods, as well as any furtherapplication of the principles of the present disclosure that would beapparent to one skilled in the art are encompassed by the presentdisclosure even if not explicitly discussed herein. It is alsorecognized that various presently unforeseen or unanticipatedalternatives, modifications, and variations of the present disclosuremay be subsequently made by those skilled in the art. All suchvariations, modifications, and improvements that would be apparent toone skilled in the art to which the present disclosure relates areencompassed by the following claims.

1. (canceled)
 2. A prosthetic meniscus device for placement in a kneejoint, the prosthetic meniscus device having a substantially ellipsoidalshape and comprising: a central portion having an upper femur-contactingsurface for engagement with a portion of a femur and an opposing lowertibial-contacting surface for engagement with a portion of a tibia, thecentral portion comprising a resilient material; an outer portionsurrounding the central portion and having an increased thicknessrelative to the central portion, the outer portion comprising aresilient material with a reinforcement material embedded in theresilient material of the outer portion, the reinforcement materialdisposed circumferentially around the central portion, wherein the outerportion further comprises a retention structure sized and shaped toprevent posterior migration of the prosthetic meniscus device in theknee joint, wherein the retention structure comprises a pocket formed ona posterior sidewall of the outer portion and configured to receive aposterior remnant of the meniscus, wherein the pocket is disposedbetween a posteriorly extending fork portion of the posterior sidewalland a vertical portion of the posterior sidewall, wherein the forkportion is disposed inferiorly to the pocket and the vertical portion isdisposed superiorly to the pocket, wherein the pocket comprises aconcave shape defined at least in part by a superior surface of the forkportion and a surface of a surface of the vertical portion, wherein thefork portion defines a plow blade shape configured to slide under atleast a portion of the posterior remnant, wherein the fork portioncomprises a leading lower edge and the vertical portion comprises anupper edge, wherein the leading lower edge extends further posteriorlythan the upper edge, and wherein the retention structure is configuredto inhibit extreme movement of the prosthetic meniscus device within theknee joint while permitting free floating of the prosthetic meniscusdevice over a significant range.
 3. The device of claim 2, wherein thesuperior surface of the fork portion and the surface of the verticalportion extend at an angle relative to one another.
 4. The device ofclaim 2, wherein the leading lower edge extends further posteriorly thanthe upper edge by approximately 5 mm.
 5. The device of claim 2, whereinthe retention structure further comprises an enlarged anterior flangeconfigured to engage an anterior portion of at least one of a tibia or afemur in the knee joint to inhibit the posterior migration.
 6. Thedevice of claim 5, wherein the anterior flange has a height that is atleast 30 percent greater than a posterior height of the meniscusprosthetic device.
 7. The device of claim 2, wherein the retentionstructure further comprises one or more tethering extensions extendingfrom the outer portion of the prosthetic meniscus device.
 8. The deviceof claim 7, wherein the tethering extensions are loops.
 9. The device ofclaim 7, wherein the tethering extensions are fiber reinforced tabs.